The subject of the present invention is a cylinder head gasket for an internal combustion engine.
A cylinder head gasket is intended to be mounted between the engine block and the cylinder head of an engine, so as to provide sealing at the combustion chambers and sealing against the fluids, particularly the liquid used to cool the engine and the liquid used to lubricate the engine.
The sealing conditions differ according to whether the sealing is against the high-temperature gases around the combustion chamber or against the fluids outside the combustion chambers.
Thus, sealing against gases is achieved by metal firing rings, while sealing against the fluids is achieved using beads of elastomer.
The production of cylinder head gaskets using metal plates which constitute the core of the gasket is already known. The beads of elastomer intended to seal against the fluids are arranged on both sides of the gasket, for example using screen printing techniques or overmoulding techniques, inside grooves formed on the two sides of the plate.
While these elastomer beads provide good sealing against fluids, they have the drawback of being vulnerable when the gasket is cramped between the engine block and the cylinder head. Specifically, if the clamping force exceeds a predetermined value, the beads burst and lose their sealing function. To avoid this damage, tightening limit stops need to be provided on the gasket.
The object of the invention is to provide a cylinder head gasket obtained from a low number of elements, and which has excellent sealing properties both with respect to gases and with respect to fluids.
To this end, the cylinder head gasket to which the invention relates, of the type comprising metal plates forming the core of the gasket and elastomer beads intended to seal against fluids, such as the cooling water and the oil, is characterized in that it comprises:
two superimposed similar metal plates, each of which comprises a central main part and a peripheral part which are separated from one another by a slot intended to house a bead of sealing elastomer, the two parts of each plate being locally connected by bridges,
one and the same bead of sealing elastomer protruding from both sides of the gasket, lining the coincident slots of the two superimposed metal plates,
means for laterally immobilizing the two metal plates.
This gasket is of a simple structure insofar as it is made up of only three elements, two metal plates and an elastomer bead. The elastomer bead which joins the two metal plates together provides sealing against fluids by being trapped within the metal plates, allowing these plates to act as the tightening limit stop.
To ensure continuity of the sealing bead, the bridges of the two metal plates alternate from one plate to the other, so that when the two plates have been assembled these bridges occupy offset positions, and the bridges of each metal plate are offset with respect to the mid plane of this plate, so that they lie approximately mid-way through the thickness of the gasket when the two metal plates have been assembled.
According to another feature of the invention, the means for laterally immobilizing the two metal plates consist of corresponding bosses formed in these plates and intended to nest together when the two plates are superimposed. These means for laterally immobilizing the two plates come into effect before the two plates are joined together by the bead of sealing elastomer.
Advantageously, to allow the gasket to deform correctly without experiencing deterioration, each sealing bead when viewed in cross section, exhibits at least one rib protruding from each side of the gasket, and at least one rib set back from each side of the gasket.
According to another feature of the invention, the two metal plates comprise ribs which face away from each other, constituting the firing rings surrounding the openings corresponding to the combustion chambers.